A front AV projector device which has been used for business is gaining ground in a consumer market of a home theater system, for example, with the development of a low-price liquid crystal projector. In the liquid crystal projector, a size thereof has rapidly been reduced and a price thereof has been reduced by improving a degree of integration of components. In addition, a resolution has also been improved with VGA, SVGA, XGA, and SXGA because of the progress of a personal computer, and so a micro-lens array substrate that projects an image of a liquid crystal monitor by efficiently using light from a light source is required also with the improvement in the resolution of the liquid crystal monitor installed in the liquid crystal projector.
In this micro-lens array substrate, a degree of integration of a micro-lens has also been improved in accordance with the improvement in the resolution of the liquid crystal monitor. The micro-lens needs to cope with higher-definition concurrently with higher-brightness; and when a panel size of a liquid crystal display element, for example, becomes small, a pixel size becomes minute proportionally thereto, and therefore an array pitch of the micro-lens itself becomes also small. Accordingly, there is a necessity to make a cover glass thin.
In the past, an application of a wet etching method, a 2P (Photo-Polymerization) method, and the like using a quartz substrate or various glass substrates has been put into practical use for a production of such micro-lens array substrate.
A method for manufacturing a micro-lens array substrate using the wet etching method is shown in FIG. 17. First, a resist mask 32 having a plurality of circular openings 32a correspondingly to the micro-lens array is formed on a substrate 31 made of glass or quartz as shown in FIG. 17A. Next, a plurality of lens-shaped concave portions (spherical concave portions) 33 are formed in a surface of the substrate 31 by isotropic etching through the resist mask 32 using an HF system etchant as shown in FIG. 17B. Next, after the resist mask 32 is removed, the substrate 31 is coated with a resin 34 whose refractive index is different from that of the substrate to fill the concave portion 33 with the resin 34 as shown in FIG. 17C. A micro-lens array 36 in which a plurality of micro-lenses 35 are consecutively arrayed is formed by the resin 34 in the concave portion 33 and the substrate 31. Then, a cover glass plate 37 is bonded on the substrate 31 through the resin 34 and is polished until a required thickness, and further a transparent electrode 38 of ITO (Indium Tin Oxide), for example, is formed on the cover glass plate 37 as shown in FIG. 17D and so a micro-lens array substrate 39 is produced.
A method for manufacturing a micro-lens array substrate using the 2P method is shown in FIG. 18. First, a stamper 41 shown in FIG. 18A is prepared in which a micro-lens array shape 43 having a plurality of micro-lens shapes 42 arrayed is integrally formed. Next, a first resin layer 45 is formed on a glass substrate 44, and the micro-lens array shape 43 of the stamper 41 is pressed onto the resin layer 45 as shown in FIG. 18B. Subsequently, the stamper 41 is detached, and thereby a concave portion 46 of the micro-lens array shape is transferred to a surface of the first resin layer 45 as shown in FIG. 18C. Next, the first resin layer 45 is coated with a second resin 47 whose refractive index is different from that of the first resin to fill the concave portion 46 with the second resin 47 as shown in FIG. 18D. A micro-lens array 49 having a plurality of micro-lenses 48 arrayed is formed by the first resin layer 45 and the second resin 47. Subsequently, a cover glass plate 50 is bonded on the glass substrate 44 through the second resin 47, and the cover glass plate 50 is polished until a required thickness as shown in FIG. 18E. Thereafter, a transparent electrode 51 of ITO (Indium Tin Oxide), for example, is formed on the cover glass plate 50 to produce a micro-lens array substrate 52.
A method for manufacturing the micro-lens array substrate using the above-described wet etching method is described in the patent reference 1. In addition, a method for manufacturing the micro-lens array substrate using the 2P method is described in the patent reference 2.
[Patent reference 1] Japanese Published Patent Application No. 2000-231007
[Patent reference 2] Japanese Published Patent Application No. H09-258195
The method for manufacturing the micro-lens array substrate using the above-described 2P method is excellent in mass productivity since the lens shape is transferred to the resin layer 45 by using the stamper 41 in the method. However, it is difficult to control a pattern size of the micro-lens array due to a thermal shrinkage of the resin layer 45 at the time of hardening. In addition, since the concave portion 46 is formed in the resin layer 45, an acute angle cannot be maintained but tends to become round in a boundary portion of the adjacent concave portions 46, that is, at a vertex portion 53 (refer to FIG. 18D), and as a result, the boundary portion becomes a non-lens area. Particularly, when the micro-lens itself is made minute in order to obtain higher resolution, a ratio of this non-lens area increases and it becomes difficult to form the micro-lens array. Also, there have been limits in thermostability and light stability since two kinds of resins are used.
In the method for manufacturing the micro-lens array substrate using the wet etching method, the shape of a micro-lens only becomes spherical since this method is the isotropic etching, and it is not possible to form a micro-lens of other aspheric shapes. That is, there is no controllability upon the lens shape.
On the other hand, in the past, there has been a limit of 30 μm for a cover surface layer thickness that is a thickness from the vertex portion of the concave-shaped lens of the resin layer to the surface layer of the cover glass plate, and it has not been possible to form the thickness thinner than this . A reason therefore is that the resin layer cannot be formed thin due to an influence of a viscosity of resin when forming the resin layer (in actuality, a resin whose viscosity is higher than 100 cp was used).
Further, when the micro-lens array 36 is formed in the above-described quartz substrate or glass substrate, and when this micro-lens array substrate 31 is filled with the resin 34 to be hardened after the cover glass 37 is bonded, an air bubble 30 is generated at a peripheral portion of the micro-lens array 36 formed as shown in FIG. 19. The air bubble 30 is generated due to an occurrence of a distortion by the shrinkage of the resin in the area of micro-lens array 36 and in the peripheral portion, and also due to an occurrence of an abrupt change in the resin thickness. In the case of the micro-lens array substrate using the 2P method, an air bubble is similarly generated between the first resin layer and the second resin layer in a peripheral portion of the micro-lens array area. Even though no air bubble is generated, there is an occasion that a glitter appears on a screen due to the distortion as if the air bubble is generated.